Generally, the present invention relates to radiotherapy and more particularly to a procedure that creates a three dimensional picture of a location or area in the body of a patient to be treated, such as a tumor. Radiotherapy generally involves the use of an external beam with a linear accelerator, which largely delivers photons (γ-radiation). Neutron beam radiotherapy is used for some tumors with a narrow tissue margin. Electron beam radiotherapy has a very short tissue penetration and is typically used for skin or superficial cancers. Proton therapy can provide very narrow depth of field exposure with sharp margins.
Typically the patient undergoes a CT (Computerised Tomography) scan of the location to undergo treatment in a proposed treatment position. The images from this scan are transferred to a computer to plan the patient treatment, and the physician traces the outline of the tumor and normal organs on each slice of the CT scan. The treatment planning computer allows the physician to try different beam arrangements on the patient, a process sometimes referred to as virtual simulation. The treatment planning computer may show the beam's eye view (BEV), which is a visual depiction of the treatment field in relation to the tumor and the bony anatomy of the patient as well as normal organs. Using information from the BEV, physicians can design custom blocking of parts of the radiation beam in order to protect normal tissue as much as possible. This allows doctors to provide the highest possible dose of radiation to the tumor.
One form of radiotherapeutic treatment is known as Intensity-Modulated Radiation Therapy (IMRT) which utilize machines that are a specialized case of three dimensional conformal therapy that allow for the modulation of certain intensities associated with a specific beam-angle configuration such that any radiosensitive organs that the beam passes through are subjected to a diminished dose. Another treatment is known as Image Guided Radiation Therapy (IGRT) where the electron beam machines have a CT scanner integrated with the treatment system, or an X-Ray Tube and a Si-detector mounted on the gantry of the linear accelerator. The patient can be scanned and the tumor located in three dimensional space immediately before treatment. The ability to correct for movement and setup errors allows smaller margins to be used, protective healthy tissue and escalating the tumor dose.
Most of the new equipment used in radiotherapy have the ability to provide very precise adjustment to the orientation of the beams produced and the target to be treated. Most of the adjustment/aligning techniques use computerization to control finite variation in the x, y, and z axes. Such adjustments control the rotational and planar alignment, for example, of the gantry section of the radiation equipment and or the treatment couch on which the patient is located. The advances that have occurred in radiotherapy technology permit the use of volumetrically acquired anatomic information to plan a course of radiation therapy. Beams can be shaped according to the projection of the target along the beam's axis with appropriate adjustments for anatomic routes of tumor spread and anatomic barriers to tumor spread. This three dimensional conformal radiation therapy (3DCRT) can decrease normal tissue toxicity through shielding otherwise unshielded normal tissues. A further extrapolation of 3DCRT and the use of computer technology to determine beam apertures and fluences is intensity modulated radiotherapy (IMRT), which has also been used to conformally deliver radiation doses to the planned target volume. IMRT can further reduce radiation doses to the normal tissues surrounding a target. This increase in the ratio of the dose given to the target relative to the dose given to normal tissues can reduce normal tissue radiotherapy toxicity. This increased ratio of dose in the target as compared to the normal tissues also allows increased radiation doses to the target, while maintaining the same dose to the adjacent normal tissues to achieve better tumor control with the same level of normal tissue toxicity. All of these adjustments are designed to assure that the actual treatment with the beams precisely follows the plan for the treatment prepared by the physicians and technologists. However, treatment position setup errors often introduce variations in the position of the treatment target relative to the planned radiation beams. These errors can also be introduced by the movement of a target relative to setup marks or to other relevant landmarks that are used to position a patient for radiotherapy. Such variations can cause dose deviations from the planned doses and result in sub-optimal treatments where the entire target is not irradiated or a critical structure receives more than the desired radiation doses. Clinically available technology for image guided radiotherapy can detect variations of target position. For example, a number of image guided radiotherapy techniques have various attributes and shortcomings. These techniques include ultrasound systems, an array of infrared-reflecting surface markers, electronic portal imaging systems using bony landmarks or implanted radio-opaque markers as aids to visualization, kV imaging systems registered to the machine isocenter, and in-room CT systems.
Several specially designed IGRT radiotherapy delivery systems (e.g., Cyberknife, Novalis system, and the like) have been introduced and utilized to address the target motion and shift problems. For most of linear accelerator based treatment machines, target shift corrections are mainly achieved geometrically by moving the treatment couch with appropriate amounts of translational motion, namely, in the vertical, longitudinal and lateral directions together with rotation of the treatment couch. However, in reality, a more accurate correction of the target shift involves not only the three translational movements, but also three rotational movements. However, almost all treatment couches in clinical use can only rotate in one direction, so that a complete and accurate correction of a target shift cannot currently be achieved by couch movements alone.
Notwithstanding the advent of these recent systems there is great need to provide a method for readily correcting positioning error to assure the precisely planned treatment dose and topology is provided to the patient.
Accordingly, it is an object of the present invention to provide a means for quickly and accurately correcting for a deviation of the treatment procedure and the planned procedure. It is a further object of the present invention to provide a number of transformations matrices that will permit rapid deployment into the computer control systems of clinical radiation facilities.